1. Technical Field
The present invention relates to an illuminating device using a lamp and a projector provided with a light modulating device, such as a liquid crystal display panel, illuminated by the illuminating device.
2. Related Art
There has been proposed an optical system for a projector that includes a pair of dichroic mirrors for separating white light emitted from a projecting light source into red, blue, and green light beams, an optical path refracting mirror, serving as an infrared ray filter provided on an optical path of the separated red light beam, and an optical path refracting mirror, serving as an ultraviolet ray filter provided on an optical path of the separated blue light beam (see JP-A-2-253291).
Further, there has been proposed another optical system for a projector in which a pair of fly eye lenses for uniformizing light are arranged in front of a light source lamp, one surface of a front fly eye lens on which light is incident is a convex surface, and a filter for reflecting infrared rays is formed on the convex surface (see JP-A-10-161241).
In the former optical system, a filter is formed on an inclined mirror arranged on an optical path of the separated light beam. In this case, generally, the inclined mirror is inclined at an angle of 45° with respect to an optical axis. In this structure, the area of the filter needs to be 21/2 times larger than that when the filter is arranged orthogonal to the optical axis. That is, it is necessary to increase the area of the filter as the tilt angle of the mirror becomes larger, which results in an increase in manufacturing costs.
In the latter optical system, the filter is formed on the convex surface of the fly eye lens. In this case, since light is incident on the filter at various angles, the filter may not filter some light beams. That is, the filtering efficiency of the filter is lowered, which causes an increase in the amount of ultraviolet rays or infrared rays passing through the filter.